Experiment 4

AIM: Implementation of Echo server using socket.

THEORY:

Socket Programming is a method to connect two nodes over a network to establish a means of communication between those two nodes. A node represents a computer or a physical device with an internet connection. A socket is the endpoint used for connecting to a node. The signals required to implement the connection between two nodes are sent and received using the sockets on each node respectively. State Diagram for Server and Client Model We can understand the role of sockets in establishing a connection between two nodes over a network with the help of the following diagram:

CODE:

#include <stdio.h>

#include <stdlib.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <unistd.h>

#define BUFLEN 1024 /* Buffer length */

int main(int argc, char **argv) {

int n, yes = 1;

int sd, new_sd, client_len, port;

struct sockaddr_in server, client;

char buf[BUFLEN];

if (argc < 2) {

fprintf(stderr, "Usage: %s <port>\n", argv[0]);

exit(1);

}

port = atoi(argv[1]);

/* Create a stream socket */

if ((sd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {

perror("Socket creation failed");

exit(1);

}

/* Allow reuse of address and port */

if (setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(yes)) == -1) {

perror("setsockopt");

exit(1);

}

/* Configure server address struct */

server.sin_family = AF_INET;

server.sin_port = htons(port);

server.sin_addr.s_addr = inet_addr("127.0.0.1");

/* Bind the socket */

if (bind(sd, (struct sockaddr *)&server, sizeof(server)) == -1) {

perror("Binding failed");

exit(1);

}

/* Listen for client connections */

if (listen(sd, 5) == -1) {

perror("Listen failed");

exit(1);

}

printf("Server is listening on port %d...\n", port);

while (1) {

client_len = sizeof(client);

new_sd = accept(sd, (struct sockaddr *)&client, (socklen_t *)&client_len);

if (new_sd == -1) {

perror("Accept failed");

continue;

}

n = read(new_sd, buf, sizeof(buf));

buf[n] = '\0';

printf("Message received from client: %s\n", buf);

write(new_sd, buf, n);

close(new_sd);

}

close(sd);

return 0;

}

OUTPUT:

CONCLUSION:

The server-client socket program demonstrates inter-process communication (IPC) over a TCP/IP network. The server listens on a specified port, accepts client connections, receives a message, and echoes it back. The client establishes a connection, sends a message, and receives the echoed response. This implementation ensures reliable communication using the TCP protocol, which guarantees error-free, ordered, and complete data transfer. Such socket programming techniques are widely used in network applications, web servers, chat applications, and distributed systems.